1. Field of the Invention
The present invention relates to a receiving apparatus, a receiving method, a communication method and a transmission apparatus that receive data separated in to a plurality of fragments.
2. Description of the Related Art
Internet Protocol (hereinafter: IP) has been well used in network layer (internet layer) of computer networks. The Internet Protocol stipulates transmitting an IP datagram separated into parts called fragments by the transition apparatus, and reassembling the fragments received by the receiving apparatus as described in RFC791 “Internet Protocol” (www.ietf.org/rfc/rfc0791.txt).
The fragmenting and reassembling of IP datagram are processes conducted for enabling large packet transmission through a communication path, even when a communication link that only allows small packets, is included in the communication path.
In case of conducting fragmenting and reassembling of IP datagram on received data, the receiving apparatus has to recognize which fragments have been received and which fragments have not being received.
The identification of already received fragments is usually conducted using the fragment block hit table (hereinafter: bit table) as described in RFC791. Bit table is a table with each byte in the bit table having a correspondence to a data fragment that constructs the IP datagram. Receiving apparatus set a byte (as an example setting to “1”) of the bit table responsive to the received fragment, allowing identification of the already received fragments.
In case of conducting bit table base reassembling, the data receiving apparatus needed to reserve 8192 byte size bit table. This is due to the fact that the maximum payload of the IP datagram is 64K and the minimum size of the fragment size is 8 byte, while data receiving apparatus unable to know the size of the IP datagram and fragment size. Payload of IP datagram size can be in the range lower the 64K, and fragment size can be in the range higher than 8 byte. However, if 64K byte IP datagram is being separated in to 8 byte units, receiving apparatus need to reserve 8192 (64 Kbyte/8 byte) size bit table.
As explained above, in conventional architecture, even in case IP datagram size is less than 64K and/or fragment size is more than 8 byte (as a example 1K byte) the receiving apparatus need to reserve a bit table in the size of 8192. However, a limitation such as above, in case the payload of IP datagram is less than 64 or in case the fragment size is larger than 8 bytes, creates wasteful reservation of memory for the bit table.
Moreover, because reassembling process is a process associated with a heavy processing load, the process has to be implemented on high speed and expensive SRAM and the like. Thus, the conventional bit table area reserving architecture is possibly allows wasting expensive SRAM areas.